FIG. 1 shows an exhaust gas re-circulation control device. In FIG. 1, reference numeral 1 denotes an internal combustion engine, 2 is an intake pipe allowing inflow if air to the engine, 3 is an intake manifold allowing inflow if air to each pipe branching from the intake pipe 2, 4 is an air cleaner provided upstream of the intake pipe 2, 5 is an injector which is provided in the intake pipe 2 and injects fuel. Air entering the intake pipe 2 through the air cleaner 4 flows into the engine 1 together with fuel supplied from the injector 5.
6 represents a throttle valve which varies the degree of air intake into the engine 1 and 7 is a idle rotation speed control valve provided in the passage which bypasses the throttle valve 6. The gas mixture which enters the engine 1 is ignited by an ignition plug not shown in the figure. After combustion, the exhaust gases are expelled into the atmosphere through the exhaust pipe 8 after being purified in the purification device 9 comprised by a catalytic converter. 10 is a flow control valve which is disposed in the exhaust gas re-circulation passage 17 which is connected to the inlet and outlet sides of the intake manifold 3 The flow control valve drives the stepping motor which controls the flow of exhaust gases.
11 is an electronic control unit which generates control signals to the flow control valve 10 on the basis of information received from the driving state detection means comprised of elements such as a throttle aperture sensor 12 which detects the degree of aperture of the throttle valve 6, a pressure sensor 13 which detects the pressure in the intake pipe, a water temperature sensor 14 which detects the temperature of the engine cooling water, and the ignition device made up of the ignition coil 15 and the igniter 16.
FIG. 2 is a front view showing the above flow control valve, FIG. 3 is a longitudinal section view of FIG. 2 taken along the line A--A. 21 is a valve housing having an inlet port 21a which communicates with the engine exhaust gas pipe 8, an outlet port 21b which communicates with the engine inlet pipe 2 and a passage 21c between the inlet port 21a and the outlet port 21b. 22 is a valve seat provided in the passage 21c of the valve housing 21. 23 is a valve body which opens and closes the aperture of the valve seat 22. 24 is a valve shaft on one end of which the valve body 23 is mounted and which displaces the valve body 23 to the open and closed position by reciprocating motion as a valve rod. 25 is a bush which acts as a bearing for the valve shaft 24 mounted in the valve housing 21. 27 is a spring holder mounted on the other end of the valve shaft 24 which projects externally from the valve housing 21.
28 is a bracket formed as a unit with the valve housing 21 by cast iron for example on the side from which the valve shaft 24 projects from the valve housing 21. The bracket 28 is a cup shaped element of a fixed height which is sunken in a truncated cylindrical concave shape on the step motor 29 side.
A flange element 28b which mounts the stepping motor 29 is formed on the stepping motor 29 side of the bracket 28 through the holder 30. A screw hole 28c which hinges the mounting screw 32 is provided in the flange 28b. The cross sectional size of the flange 28b is of a size having the minimum necessary strength to support the stepping motor 29 or is a slightly larger size (for example a size having a surface area twice that of the necessary strength.)
Furthermore in the bracket 28, a large aperture 28d is formed which communicates with the lower face of the indented part 28a and, on the valve housing side 21 of the bracket 28, there is a holder 26 which prevents the build-up of deposits within the vertical range of the bush 25 displaced by the valve shaft 24.
The motor holder 30 is made from material having good thermal conductivity. A cylindrical member 35 which is suspended into the inner part of the indented part 28a of the bracket 28 is formed so as to cover the outside of the coil spring 52 and the spring holder 27. A plurality of heat radiating fins 35a are provided on the outside face of the cylindrical member 35.
Next the components of the stepping motor 29 will be explained. 36 is a hollow motor housing, 37 is a rotor which is supported in free rotation by an upper bearing 38 and a lower bearing 33 at its upper and lower ends. A magnet 39 is mounted on its outside periphery. The central part of the rotor 37 is hollow, displaces vertically and has a threaded section 37a formed on its inner face.
40a and 40b are upper and lower yokes which are mounted on the inner part of the motor housing 36 so as to face the magnet 39 of the rotor 37 and in the inner part of which are housed bobbins 41a and 41b. 42a1 and 42a2 are coils wound around the bobbin 41a, 42b1 and 42b2 are coils wound around the bobbin 41b and 43 is a plate magnetically separating the upper and lower yokes 40a and 40b. 44 is an upper bearing seat 45 is an actuator rod which is supported in a hinged state by the threaded section 37a of the inner part of the rotor 37 and projects downwardly from the motor holder 30. The tip of the actuator rod 45 displaces vertically and pushes against the valve shaft 24.
Due to the fact that the actuator rod 45 is prevented from rotating by the bearing of the actuator rod and the motor bush 54 which has a rotation prevention function, the actuator rod displaces vertically in response to the rotation of the rotor 37. A stopper 45b is provided in the actuator rod which contacts with and detaches from the stopper 37b of the rotor 37 and limits displacement above a fixed amount. 46 is a SPL washer for providing pre-load to the lower bearing 33. 51 is a connector which supplies electrical pulses to each coil.
As shown in FIG. 4, the connector 51 comprises the terminals 1-6 which are electrically connected to the coils 42a1, 42a2, 42b1, 42b2, and the connector housing 51a. Transistors Tr1-Tr4 are connected on the earthing line of the terminals 1, 3, 4, 6.
Terminal 2 one end of which is connected to the coils 42a1 and 42a2 and terminal 5 one end of which is connected to coils 42b1 and 42b2 are connected to the electrical supply terminal +B through the switch SW. The connector housing 51a and the motor housing 36 are formed as a unit by resin.
52 is a coil spring which intercalates between the spring holder 27 and the bracket 28. The coil spring pushes the valve shaft 24 upwardly towards the middle of the figure against through the spring holder 27 and maintains the valve body 23 in a closed state. While in a closed state, a gap is formed between the valve shaft 24 and the actuator rod 45 and the valve body 23 is maintained in an accurately closed state.
Next the operation of the flow control valve will be explained. The rotor 37 of the stepping motor 29 which acts as a motive source does not rotate continuously but only makes a single rotation. Firstly if an electrical current is applied to the top of the coils 42a1 and 42a2 in an anti-clockwise direction viewed from above, the upper face of the coils will be a north pole N, the lower face will be a south pole S and the stator will be a north pole. In the same way if a current is applied to the lower face of the coils 42b1 and 42b2, a magnetic pole will be generated in the stator. As a magnet is provided which is minutely divided into S poles and N poles in the rotor, it is stabilized in the stator. Actually as shown in FIG. 5 one step at a time is rotated by changing the phase in a sequential manner. For example when the valve body 23 is opened, the phase is changed in the sequence 0.fwdarw.1.fwdarw.2.fwdarw.3.fwdarw.0.fwdarw.1, when in the closed position the phase is changed in the sequence 0.fwdarw.3.fwdarw.2.fwdarw.1.fwdarw.0.fwdarw.3.
In response to the rotations of the rotor 37, the actuator rod 45 which is hinged to the threaded section 37a of the rotor 37 moves downwardly in the figure, is repelled by the elastic force of the coil spring 52 which is compressed between the bracket 28 and the spring holder 27, displaces the valve shaft 24 downwardly and opens the valve body 23.
In such a way, the flow of the high temperature engine exhaust gases on the inlet port side 21a of the housing 21 is controlled by the valve body 23 and is directed to the outlet port side 21b through the passage 21c.
Furthermore since generating poles of the stator rotate in the opposite direction if the conducting phase order with respect to the coils 42a1, 42a2, 42b1, 42b2 is changed, the rotor 37 is rotated in the opposite direction to the above. In response to the direction of rotation of the rotor 37, the actuator rod 45 displaces upwardly towards the middle of the figure. As a result, the valve shaft 24 displaces upwardly towards the middle of the figure due to the coil spring 52 and the valve 23 closes. When the stopper 45b reaches the stopper 37b of the rotor 37, the displacement of the actuator rod 45 terminates.
Since the conventional flow control valve is constructed as above, the cylindrical member 35 covers the periphery of the actuator rod 45 and the valve shaft 24 and has the function of protecting the slidable parts of the stepping motor 29 and the valve housing 21 from foreign objects. In other words, foreign objects such as dust or muddy water penetrate from the aperture 28d into the indented part 28a of the bracket 28. Such foreign objects try to enter the slidable parts of the valve shaft 24 and the bush 25 or the hinged part of the actuator rod 45 and the rotor 37. However since the periphery of the actuator rod 45 and the valve shaft 24 is covered by the cylindrical member 35, the foreign objects can not reach the above regions and the lodgment or deposition of outside objects into the slidable or hinged parts of the valve shaft 24 or the actuator rod 45 is prevented.
In order to prevent the entry of outside objects such as dust or muddy water into the valve shaft or the spring on its periphery, the tip of the cylindrical member must abut closely with the lower face of the indented part 28a of the bracket 28 (hereafter called the lower face of the bracket), and totally close the gap L1. However closing the gap L1 creates the problems of the application of radiant heat from the valve housing side 21 or the liability to heating.
As a solution to this problem, an aperture 28d, provided in the bracket, on the side of the motor separated from the lower face of the bracket has been provided. However even though the tip of the cylindrical member is separated from the valve housing, it is possible to prevent the entry of foreign objects by the bracket itself. On the other hand water which has penetrated the lower face of the bracket accumulates and enters one end of the coil spring which leads to the generation of rust and reductions in durability.
The present invention is proposed to solve the above problems and reduce both the effect of heat from the valve housing and undesirable effects due to the penetration of foreign objects by the provision of a member on the periphery of the spring such as a spring seat.